Conventionally, heat of the turbine exhaust gas in a gas turbine cycle has been recovered by means of preheating air or withdrawal of refrigerative energy by means of absorbent type refrigerant or generation of steam by a waste heat boiler. In addition, in some prior art gas turbine cycles, air preheating is carried out through a mixture of air/steam which is obtained by injection of water into compressed air.
The following publications teach the regenerative cycle of water injection type gas turbines; The U.S. Pat. No. 2,095,991, No. 2,115,112, No. 2,115,338, No. 2,678,532 and No. 2,869,324, Swiss Pat. No. 457,039, and French Pat. No. 1,007,140.
Other publications, reporting on these patents include "Gas Turbines with Heat Exchanger and Water Injection in the Compressed Air", Combustion vol. 44, No. 6, December 1972, p. 32-40, by N. Gasparovic et al. (hereinafter referred to as report A) and Combustion vol. 45, No. 6, December 1973, p. 6-16 (hereinafter referred to as report B).
Each of the above-mentioned patents discloses the method of heat recovery by the use of a mixture of compressed air/steam with a description of the process of injecting water to be mixed with the compressed air or with the intermediately compressed air. Reports A and B state in reference to these patents that the increase in thermal efficiency attainable with each of them has been proved to be about 1.5 times that for conventional simple gas turbine cycles in spite of great increases in the specific power. These achievements are not completely satisfactory; rather, they are poor from the viewpoint of the utility and practicability of general power generation as reflected in the concept of a combined cycle of gas turbine and steam turbine. With the recent dramatic increase of fuel prices (by 20 times in 10 years), the direction of the development of a more effective power generating plant capable of a significant increase in thermal efficiency has taken a general turn toward the possibility of embodying a combined cycle gas turbine and steam turbine.
The applicants of the present invention have found that an increase of thermal efficiency is achieved by the system in which heat recovery of turbine exhaust gas is carried out by an MPC mixture of compressed air/water/steam which is obtained by injection of water into a part of or the whole of compressed air, and filed several applications such as Japanese patent application No. 55-78808 on the basis of the above discovery.